A disk-type apparatus has a support defining three generally parallel and equispaced axes surrounding a central axially extending twisting region. Respective shafts lie on these axes and are journaled in the support for rotation about the respective axes. Each shaft carries a respective set of axially spaced disks. The disks of each set are offset from the disks of the other sets so that the rims of these disks can radially overlap at the twisting region. A pair of yarn eyes axially flanks the sets of disks in axial alignment with the thread-twisting region. Thus a yarn to be false-twisted can pass axially through one of the eyes, then axially along the twisting region in contact with the disks, and then axially through the other eye. During the false-twisting operation the disks are all synchronously rotated in the same angular direction so that their rims in contact with the yarn impart a false twist to it. Such an arrangement has proven itself extremely practical and effective.
Threading the yarn to be false twisted through such an apparatus is a relatively complex operation, as the yarn passes in a zigzag through the thread-twisting region while contacting each of the disks. Just pushing the yarn into the nip between two of the sets of disks is ineffective, as at such a nip the rims of one of the sets will be moving outwardly while the others will be moving inwardly, so that forcing the yarn inwardly in this manner is impossible.
Accordingly recourse has been had to a system such as described in U.S. Pat. No. 3,911,661 of Oct. 14, 1975. In this arrangement the disks are spaced relatively far apart axially and a threading device is provided having a plurality of arms that extend into the thread-twisting region adjacent the shaft of one of the sets of disks. These arms are positioned so that they hold a filament against the inwardly traveling rims of one set of disks while holding it out of contact with the adjacent outwardly traveling rims. This arrangement has two principal disadvantages. First, it requires the apparatus to be relatively tall, as considerable axial spacing is needed between the disks to allow the device to function by holding the filament out of contact with the outwardly traveling rims. Second, such an arrangement brings the yarn which is at a standstill into contact at a single instant with a plurality of traveling rims, while at the same time forcing the yarn to move from a straight path to a zigzag path. This abrupt change in speed and path frequently breaks the yarn.
German printed Pat. applications Nos. 2,606,198 and 2,607,290 show another system wherein the eyes axially flanking the sets of disks are displaceable between an inner position axially alligned with the twisting region and an outer position spaced outwardly therefrom. The device employs separate electrical motors for synchronously driving the respective shafts carrying the sets of disks. To load a yarn into the device the eyes are swung outwardly and a yarn is threaded through them along the edge of the apparatus. Then the yarn is moved inwardly between the nip of two sets of disks to a position extending along the twisting region. During this loading operation the set of disks that would have the outwardly traveling rims is arrested so that only the inwardly traveling rims are effective on the yarn being loaded in to displace it into the desired position. Although such a device does allow the vertical height of the arrangement to be reduced considerably over that of the above-described U.S. patent, it requires expensive separate drives for the various shafts, along with appropriate control equipment. Furthermore, the yarn is again brought from a standstill into engagement with the inwardly-moving rims which immediately deform it into a zigzag path, so that the likelihood of breakage with this relatively complex device is just as great as with the other above-described prior-art system.